This invention relates generally to beam intensity controllers and, more particularly, to an optical beam intensity control system which automatically controls the intensity of a beam of light independently of the source of the optical energy.
It is often necessary to control the intensity of a light source without affecting the energy source for the light generation. This occurs in such diverse applications as exposure control in photography, laser communication beam intensity control, video camera exposure limitation, laser interferometry, holography, spectrophotometry, densitometry, colorimetry and within, for example, an optical distortion analyzer system as described in U.S. patent application entitled Optical Distortion Analyzer System, Ser. No. 297,527 filed Aug. 28, 1981 by this inventor.
In general, a beam intensity controller is utilized in conjunction with a source of light which generates a fluctuating or varying intensity beam. The beam passes through the controller which compensates for the fluctuations and outputs therefrom a time invariant light field. There are many various types of controllers found in the prior art. For example, there are iris controllers in photographic cameras, Pockels cell and Kerr cell polarization modulators, liquid crystal devices and the like. Unfortunately, all of these devices have notable drawbacks.
An iris or aperture controller affects the modulation transfer function, that is, a reduced aperture not only reduces the light transmission but also reduces the resolution capability of the optical system. Polarization modulators depend upon a high degree of polarization of the generated light source.
There are other controllers which depend upon the diffraction of the incident light source such as in Bragg cells wherein an acoustic signal is used to create a diffraction grating in a solid such as a quartz. In these devices the apertures are extremely limited as only certain incident angles experience the greatest diffraction modulation. In addition, this type of procedure is wavelength dependent.
Still further prior art may include modulation through frustrated total internal reflection. However, such a procedure is also a wavelength dependent process and may depend upon the polarization. Finally, there are numerous systems which achieve intensity control by modulating the energy source. By so doing, this type of intensity control cannot be used with systems which rely upon an unmodulated source of energy.
It is therefore essential and of great importance to provide an optical beam intensity control system which not only controls the intensity of a light beam without affecting the energy source but which is also highly reliable, efficient, and does not contain the drawbacks associated with prior art intensity controllers.